For some people they occur naturally as part of their facial structure – you will sometimes seem them on young women, and even children where they are often associated with a strong cheek bone in which case they can represent a natural junction between the lip and the cheek. For many people however they occur as part of the ageing process, and get progressively deeper as time goes on.
As we age we lose volume from the cheek. Loss of volume in the cheek causes the skin to sag, which can cause a deepening of the nasolabial fold. Correction of the volume loss in the cheek can therefore often result in an improvement in the appearance of the nasolabial fold as a by-product.
Adding volume to the fold itself can be effective to reduce the depth of the wrinkle. When taking this approach however the volume added needs to be very, very conservative. This is one of the treatments that inexperienced practitioners tend to get wrong because although it is relatively easy to inject in a straight line, it is more difficult to judge when to stop and avoid over-treatment.
Facelift surgery is excellent for removing loose skin in the lower face and neck. It tends to have a very limited effect on the nasolabial fold itself however.